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Abstract:

Apparatus and methods for wire insulation in transmission line based
electric fence are described in this invention. An insulator holds a wire
pair that form the transmission line in its wire clamps. The insulator
has a rain shed that sheds the wire clamps from getting wet by rain
water. The insulator also has a pair of rain water divert guides that
guide rain water accumulated on the wire to flow to the guide instead of
to the wire clamps. This invention also describes a wire heating method
that uses electric current to heat the fence wires such that the
wire/wire clamp contact point will be kept dry and ice, snow accumulated
on fence wires will be melted. Performance of the transmission line based
electric fence can thus be greatly improved in advert weather conditions.

Claims:

1. an insulator for electric fence comprising a. wire clamps that hold
wire in position while allowing the wire to move axially; b. a rain shed
which keep rain water from wetting said wire clamps; c. a rain water
divert guide that deflects rain water such that it will not flow towards
and wet said wire clamps;

2. an electric heating system for use in conjunction with said insulator
that sends electric current through electric fence wires; a. Said
electric current may be direct current (DC) or alternative current (AC).
b. said electric current is supplied to transmission line via low pass
filters that have high impedance at higher frequencies but exhibit lower
impedance at lower frequencies or direct current. c. amplitude of said
electric current may be controlled manually or by an automatic
controller.

Description:

BACKGROUND OF THE INVENTION

[0001] Electric fences are widely used for security purposes and for
animal control. Most electric fences use metal wires to surround the area
to be protected, and the metal wires are changed to a high voltage by
energizers. When touched, this high voltage on the wires will repel or
deter the intruder or animal. And an alarm signal is also triggered by
the touch on the wire. But this type of electric fences can not give
information of the location of the intrusion.

[0002] A recently filed patent application (application Ser. No.
12/954,704) describes a new type of electric fence, which is based on
transmission line. A pair of metal wires are installed on the fence,
which is equivalent to a common transmission line with a characteristic
impedance. A short electric pulse is sent down the transmission line. If
an intruder touches the transmission line, he adds a load impedance at
this point of the line. According to the transmission line theory, a
portion of the electric short pulse will be reflected back due to
mismatched impedance. The intrusion can thus be detected and its location
can be calculated from the time needed for the pulse to travel back.

[0003] Since the characteristic impedance is a function of the separation
between the wire pair, a support element is needed every few meters to
keep this separation constant. This is because changes in this separation
lead to changes in local characteristic impedance, and hence pulse energy
reflection. A practical fence has a length from a few hundred meters to
tens of kilo meters. Therefore there will be hundreds or even thousands
support elements alone the electric fence.

[0004] For the same reason as mentioned above, it is vital for the proper
operation of this type of electric fence that the insulation between the
wire pair and between the wire and ground at each support is kept at a
high level, at least 4 orders higher than the characteristic impedance of
the transmission line, since there are up to 1000 such supports along the
whole electric fence, and more or less they all cause electric power leak
between the wire pair of between the wire and the ground. The
characteristic impedance of a wire pair transmission line is normally
between 50 ohm and 1000 ohm, and therefore the insulation of each wire
support needs to be 10 mega ohm or higher. In dry weather, this level of
insulation is no problem at all if proper materials are used for the
insulators, such as plastics, ceramic, glass, epoxy, or even wood.
However, in non idea weather, such as rainy, snowy, foggy, or humid,
days, to achieve such an insulation level becomes difficult. Dripping
rain water, condensation, or dew, snow, ice, accumulated on surface,
greatly reduce insulation resistance by orders. A reduction of insulation
level means a load is connected between the wires or between the wires
and the ground. This not only causes excessive pulse energy loss and
hence reduced workable fence length, but also leads to scattered pulse
energy reflection alone the fence, which either increases system
background noise level, or increases false alarm rate. Therefore,
transmission line based electric fences need significantly better
insulators.

SUMMARY OF THE INVENTION

[0005] This invention describes apparatus and methods to maintain high
insulation level for transmission line based electric fence in advert
weather conditions. The electric fence insulator described in this
invention comprises two wire clamps, a rain shed, and two rain water
divert guides. The clamp keeps the wire in place but allows it to move
axially such that wire tension devices can apply tension to the wire. The
rain shed sheds the wire clamp such that rain drops will not hit the
wire/wire clamp contact point. The rain water divert guide is a plastic
string, attached to the wire on both sides of the clamp, with a dip at
the middle. When rain water accumulates on the wire, it may flow towards
the wire clamp due to the not level installation of the wire, and thus
may wet the wire/wire clamp contact point. The rain water divert guide
directs the rain water toward the string dip, and thus keeps the
wire/clamp contact point from rain water.

[0006] In the transmission line based electric fence there is a possible
electric current loop. This invention uses this electric current loop to
heat the wire or wire pair, particularly to heat the wire/wire clamp
contact point. This is accomplished naturally, since the wire clamp holds
the wire and thus prevents heat from radiating into air. The raised
temperature at the wire/wire clamp contact point evaporates water
condensation. This electric current also melts possible ice run or snow
accumulated on the wires. The amount of the electric current needed to do
this can be controlled manually, or by an automatic control loop.

[0008] FIG. 2 is a side elevation showing the horizontal offset between
the two wires to prevent short circuit by rain water dripping or by ice
run.

[0009]FIG. 3 shows a method for heating the transmission line by electric
current. Heating power supply 26 is a DC or low frequency AC power
source, that supply an electric current to wire pair 24 via a pair of
inductors 25. These inductors have low impedance for DC or low frequency
AC current, but have high impedance for high frequency short pulse
generated by Transmitter 27. Capacitors 27 blocks the DC or low frequency
AC current from flowing into the Transmitter, but allow for high
frequency short pulses to pass through. Inductor 23, capacitor 21 and
resistor 22 form a resonator that exhibits an impedance identical to the
transmission line's characteristic impedance to the high frequency short
pulse, but has a low impedance for the heating current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010]FIG. 1 shows the insulator of this invention. The insulator is
mounted on the post via holes and bolts. The wire pair are attached to
the insulator by clamps and bolts. The two wires have an offset
horizontally such that rain water will not drip into a continuous line
between the two wires to form a resistive load between the wire pair.
When rain water collected on the wire flows towards the wire clamp, the
rain water divert guide guides the water to the bottom of the guide and
keeps it from wetting the wire/wire clamp contact point.

[0011] A DC or a low frequency AC power source is used to heat the
transmission line when necessary. The transmission line based electric
fence works using high frequency short electric pulses. Therefore
low-pass and high-pass electric filters that have different impedance at
different frequencies can be used to supply electric current to heat the
wires without affecting the normal operation of the electric fence. In
FIG. 3, inductor 23, capacitor 21, and resistor 22 form a parallel
resonator that exhibits the transmission line characteristic impedance at
the pulse train frequency while providing a low impedance path for a DC
or low frequency AC current to heat the wire pair. The amplitude of this
current can be controlled manually via a variable resistor, or can be
controlled by an automatic controller.